/Engine/Source/Runtime/GeometryCore/Public/Sampling/VectorSetAnalysis.h
Run simple greedy clustering algorithm on input ClusterVectors. Done in a single pass over vectors, each successive Vector is either grouped with one of the existing clusters if it's direction is within AngleToleranceDeg, or creates a new cluster.
void GreedyClusterVectors ( RealType AngleToleranceDeg )